Telegraph signaling system



H. NYQUIST TELEGRAPH S-IGNALING- lSYSTEM Oct. 9,1945.

. Filed March 4, 1945 l 1676.l 3A

UPPER .SIDEBAND ,nii Y @S F/Gzc.

v lPatented Oct. 9, 1945 I TELEGRAPHSIGNALING SYSTEM y .VHarry Nyqust,'"Millburn, N; J., assigner to Bell Telephone j Laboratories,

Incorporated, New

l York, N. Y., a corporation of NewYork l ,Application March 4, lsiaserial No; 477,986

' s claims. (01. 17e- 66) This invention relates to carrier current telegraph systems and more-particularly tov two-tone carrier telegraph systems operated,Y on asi'ngle side-band basis such that Va certain-distortion Aeffect in each signaltendsto null'ify a correspond- Aing distortioneffect in the other'signal. g y,

- In two-tone ,carrierrcnrrent telegraph systems it is -the practice to apply the output of each of two different carrier current sources toa'transmission line kfor individual spacing; and` marking signals by lmeans of a vkey or equivalent mechanism lsuch that the timeduration.oiA the individual. currents ongthe line corresponds relativelyy closely to .fthe keying action. As is Well known, the process n of connecting the kindividual 'cacrrier4 current sources to the line anddisconnecting'them thereyfrom gives rise to a band of currents Whose frequencies are Vhigher than` the frequencies of the individual carrier currentaand aha'nd of currents Whose frequencies areflower than the lfrequencies-of the individual .carrierfcurrents.- These twozbands constitute, for the individual marking andspacing signals, the upper and lowerY sidebands asl modulationy components. In `so far 'as transmitting intelligencegis concerned, onefsideband` isf'suhstantiaily .the; equivalent of the other side-band.A Hence, 'signal intelligence' mayv be` obtained by transmitting one side-band and suppressing the other'side-band for each of the spacofthe frequency band required for thetransmission of signal intelligence. v*Infsinglefside-band transmissiomhoweveri, a relatively strong'. quadra- Vvture component in the `filtered wave tendszto introduce Vbiasat the receiving end.Y vSuch .biascan topass .one side-band only, the output wave of therilter vcomprises two components, `(a) an inphase component, and V(b)I a quadrature component. For the present purpose, the in-phase component `is one Whose zeros coincide' with'.l the Vzeros of;the.steady state carrier current,'that is, is inphase with the latter current; and the quadrature component is Lone Whose zeros are a iquarterperiod out-of-phase vwith the zeros of the' steady state ,carriercurrent.A Further-discussionot'single side-r band transmission is contained in my article entitled Certain topics in telegraph-transmission theory appearing in theV transactions ,of the American Institute of Electrical Engineers, volume e?, April l928,-atpage=6l'?, and in an article entitled Effect of "the quadrature :component in singleside-band transmission by H. Nyquistand i K; W. lPiegerappearing inthe Bell System Technical Journal, volume 19,-Januarynl940, at "page 6?. In these discussions,` itis notedythatthe quadrature component is=present When the amplitude of the in-phase 'component is changing', `and tends to haveisubstantially its maximumrvalue when the amplitude of theA in-phase component is changing most rapidly. When` the. in-phase component attains Va steadyV state condition, the

` .value of the quadrature lcomponent falls substan- -tially-tofzero. Thequadrature componenttend's ving and marking signals. This reduces the Width 25, 1,930, itis,disclosedfthat'rv when aJltervisused -4 i to changethe shape of the received Ycurrent so that, in the case of single side-band transmission, -it tends to cause bias at the receiving end of" the transmission line. l It is the object of my invention tov provide ak telegraph system in which carrier currents off twoY differentfrequencies` are used to transmit spacing y and marking signals-on a single side-bandlo'asis such `that the bias; due' tothe quadrature component in eachv signal tends to nullify'the bias due tothe quadrature component in the other signal.

In a specific embodiment, the present invention .comprises a transmissiony line, means at the'sending end to apply carrier currents Yof Ydifierentitrequencies tothe line inl response to corresponding spacing'and marking signals, means at the' receiving end of the lline to detect-the receivedcarrier currents-on a 'differential basis for reproducing themarking and spacing signals; rAs the application of the different carrier currents tothe sending endl of the line and their disconnection therefrom involves the generation of upper and lower side-bands of the "individual carrier currents, a.

to the quadrature component in the other signal'.`

f A'featureof the invention relates to the. nullication of the effects of .thev quadrature comporeceiving relay is operated differentially from space-to-mark and mark-to-space so that any variation in the magnitude of eachsignal also occurs in like manner inthe magnitude, ofthe other signal.

The invention will be readily understood-.from

the following description taken together with the accompanying drawing in which: f

Fig. 1 is a two-tone telegraph circuit adaptedl for single side-band transmission;

Figs. 2A through 2D are curves illustrating certain action in Fig. 1;

Figs 3A and 3B are curves showing various modifications of Fig. 1, and

Fig. 4 is a circuit of an alternate transmitter which may be substituted in Fig. 1.

Referringto Fig. 1, a sender I0 is actuated in accordance with signal waves of direct current corresponding to the signal elements which are to be transmitted. The sender I0 controls alternately the outputs of sources II and I2- of carrier current of frequencies F1 and F2, respectively, such that discrete groups of Spacing and marking carrier currents including the upper and lower side-bands associated with each thereof are produced. A single side-bandlter F1 is interposed in the transmitting branch of the spacing current Fiffo-r passing the carrier current'F1 and either the upper or the 'lower side-band for identifying the spacing signal. A singlev sideband lter F2 is interposed in the transmitting branch of the marking current F2 for passing .the carrier current F2 and either the upper or the lower side-band for identifying the marking q signal. At the receiving end, the transmitted :and `2Cby root-means-square addition, the result of which is shown in Fig. 2D. lSince the addition of two components in quadrature to each other always gives a resultant which is greater than either component, the presence of the'quadrature component results in a bias indicated by the solid line in Fig. 2D in which be used to connect the sending and receiving terminals to the transmission line.

Fig. 2A represents the envelope of a single `reversal such as would `be obtained inthe circuit of Fig, 1 at the inputof each of the transmit-4 ting and receiving filters F1 and F2.A Results of certain action by the individual filters F1 and F2 may be represented by individual components illustrated by the curves ofFigs. 2B, 2C and 2D. In Fig. 2B=the envelope represents the in-phase component of the current received at one of the amplifier-detectors I4 and I5, and such component is assumed to be distortionless in the sense in which this term is used herein. In Fig. 2C the envelope represents qualitatively the accompanying envelope of the quadrature component which, as pointed out above, has the figure the ibrokenvline is a reproduction of the curve in Fig. 2B.

As the individual spacing and marking branches atboth the transmitting and receiving ends of the line I3 embody one single side-band filter F1, each of the spacing and marking signals transmitted and received on the line I3 possesses approximately the distortion indicatedy bytheenvelope in Fig. 2D. With the system of Fig. 1,1using two-tone single side-band'transmission, Vit is clear that the `distortion in the spacing signals' due to the presence of the quadrature component therein tends to cancel the distor-tion in the marking signals due to the presence of the quadrature component therein, and Vice versa."Tl'1is is sofor the reason that the current in the spacing Winding of the receiving relay RR tends to release the armature substantially at the saine Value at which the current in the marking winding tends to actuate the armature, and Vice versa.`

Further distortion of the envelope of Fig. 2D due to unequal attenuation of the amplitudes of the transmitted currents at a certain frequencies and the phase delay thereof is obviated by proportioning the amplitude versus frequency characteristics of the individual' lters F1 and F2 such that the cut-off is sloping and such that the individual carrier frequencies F1 and F2 lie at or near the mid-points of the sloping cut-offs as disclosed in my patent, supra. In the system of Fig. 1, it is desirable that the individual spacing and marking carrier frequenciesv F1 and F2 be located at corresponding edges of the characteristics of both single side-band filters F1 and F2 as shown in Figs. v3A and 3B.l Referring to Fig. 3A, the single side-band filters F1 and F2 pass substantially the upper side-bands of frequencies only of the respective spacing and marking signals, and the individual frequencies of the spacing and marking carrier currents F1 and F2 lie at or near the mid-points of the sloping cut-ois atthe lower edges of both characteristics. In Fig. 3B, the single side-band filters F1 and F2 pass substantially the individual lower side-bands of frequencies only but now the individual frequencies of the spacing and marking carrier currents F1 and F2 lie at or near themid-points of the sloping cut-offs at the upper edges of both characteristics. l

Fig. 4 shows an alternate transmitting apparatus which may be substitutedv in Fig. 1 for the circuit portion shown to the left of the line X-X in the latter figure. Referring to Figpl, an oscillator comprises an electron tube 2l), a parallel tuned circuit 2 I` applied across the input thereof, and a capacitor 22 applied across the control electrode and anode of the tube 20. This oscillator is provided with a further capacitor 23 interposed in its frequency controlling circuit and arranged to be cutin and out of the latter circuit of Figs. l and 4 operates in the manner describedv previously for the operation of Fig. 1 alone.

What is claimed is:

l. In a two-tone single side-band telegraph system, the method of transmitting marking and spacing signals which consists in modifying a carrier current of one frequency to produce frequencycomponents including the one carrier current frequency and upper and lower side-band frequencies for representing a marking signal,

, modifying a carrier current of a different frequency to produce frequency components including the different carrier current frequency and upper and lower side-band frequencies for representing a spacing signal, ltering said one and different carrier currents and said upper and lower side-bands associated therewith for selecting each of the carrier currents and one sideband associated therewith for identifying the respective signals, said one side-bands lying to the Yone side of the respective carrier frequencies,

transmitting the selected carrier currents and one side-bands, filtering the received carrier currents and one side-bands in a similar manner whereby a quadrature component causes bias in the respective signals, anddetecting and receiving differentially the second filtered carrier currents and one side-bands such that the bias due to the quadrature component of each signal substantially nullies the bias due to the quadrature component of the other signal.

2. In a carrier telegraph system employing marking and spacing signals, a transmission line, means at the transmitting end of said line to modify each oftwo carrier currents of different frequencies with one of said signals for producing different carrier current impulses having as frequency components the individual carrier current frequencies and upper and lower side-bands of frequencies of each thereof, a filter for each of the different signal impulses at both the transmitting and receiving ends of said line for passing current impulses whose frequencies comprise one carrier current frequency and but one of the two side-bands of frequencies associated therewith whereby marking to spacing and spacing to marking bias due I'to the quadrature components in the respective filtered signal current impulses is produced, and means at the receiving terminal to detect and receive differentially the filtered individual signal current impulses such that the bias due to the quadrature component of each filtered signal current impulse substantially cancels the bias due to the quadrature component ofthe other filtered signal current impulse.

3. In a two-tone single side-band carrier telegraph system, means at the transmitting end to produce two discrete carrier currents of different frequencies, means to modify one of said carrier currents with a marking signal to form components whose frequencies include said one carrier current Vfrequency and upper and certain lower side-bands of frequencies, means to modify the other of said carrier currents with a spacated therewith whereby marking to spacing and spacingto marking bias due to the quadrature component individual to each of the filtered signal currents is produced, said filters being provided with amplitudeversus frequency characteristics having sloping cut-offs such that the frequencies of the individual carrier currents lie at or near tthe mid-points of said cut-offs at corresponding edges of said characteristics, and means at the receiving end to detect and receive differentially the filtered signal currents, such that the bias due to the quadrature component in the filtered currents of each signal tends to nullify the bias due to the quadrature component in the filtered currents of the other signal.

4. The two-tone single side-band telegraph system according to claim 3 in which said filters for both the marking and spacing signals are provided with amplitude versus frequency characteristics to pass the lower side-band of frequencies associated with each of the modified carrier currents. l

5. The two-tone single side-band telegraph system according to claim 3 in which said filters for both the marking and spacing signals are lprovided with amplitude versus frequency characteristics to pass the upper side-band of frequencies associated with each of the modified carrier currents.

6. Thev two-tone single side-band telegraph system according to]y claim 3 in which said filters for both the marking and spacing signals are provided with amplitude Versus frequency characteristics having sloping cut-offs to pass the upper side-band of frequencies of each of the modified carrier currents, and in which the frequencies of the individual carrier currents lie at or near the mid-points of the cut-offs at the lower edges of the respective characteristics.Y

7. The two-tone single side-band telegraph system according to claim 3 in which said filters for both 'the marking and spacing signals are provided with amplitude versus frequency characteristics having sloping cut-offs to pass the lower side-band of frequencies of each of the modified carrier currents, and in which the frequencies ofthe individual carrier currents lie at or near the mid-points of the cut-offs at the upper edges of the respective characteristics.

8. In a tWo-tone single side-band telegraph system, the method of transmitting marking and spacing signals which comprises modifying a carrier wave of one frequency to produce frequency components including the one carrier wave frequency and upper and lower side-band frequencies for identifying a marking signal, modifying a carrier wave of a different frequency to produce frequency components including the different carrier wave frequency and upper and lower side-band frequencies for identifying a spacing signal, filtering the individual carrier Waves and associated side-bands to pass each carrier wave and only one of said side-bands associated therewith, and transmitting the filtered carrier Waves and one side-bands.

- HARRY NYQUIST. 

